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Abstract:

A photodiode assembly includes a semiconductor substrate, a photodiode
cell, a ground diffusion region, and a guard band. The photodiode cell
includes a first volume of the substrate doped with a first type of
dopant. The diffusion region includes a second volume of the substrate
that is doped with a second, opposite type of dopant. The guard band is
disposed in the substrate and at least partially extends around an outer
periphery of the photodiode cell. The guard band includes a third volume
of the substrate that is doped with the first type of dopant. At least
one of the ground diffusion region or the guard band is conductively
coupled with a ground reference to conduct one or more of electrons or
holes that drift from the photodiode cell through the substrate. The
guard band is disposed closer to the photodiode cell than the ground
diffusion region.

Claims:

1. A photodiode assembly comprising: a semiconductor substrate; a
photodiode cell in the substrate, the photodiode cell including a first
volume of the substrate that is doped with a first type of dopant; a
ground diffusion region in the substrate, the ground diffusion region
including a second volume of the substrate that is doped with a second
type of dopant having an opposite charge relative to the first type of
dopant; and a guard band in the substrate and at least partially
extending around an outer periphery of the photodiode cell, the guard
band including a third volume of the substrate that is doped with the
first type of dopant, at least one of the ground diffusion region or the
guard band conductively coupled with a ground reference to conduct one or
more of electrons or holes that drift from the photodiode cell through
the substrate, wherein the guard band is disposed closer to the
photodiode cell than the ground diffusion region.

2. The photodiode assembly of claim 1, wherein the commonly doped volume
of the guard band is separated from the photodiode cell by a separation
portion of the substrate that continuously extends from the photodiode
cell to the guard band and that is not doped with the second type of
dopant.

3. The photodiode assembly of claim 1, wherein the guard band includes
elongated doped regions of the substrate oriented at non-parallel angles
with respect to each other.

4. The photodiode assembly of claim 3, wherein the ground diffusion
region is joined with the elongated doped regions of the commonly doped
volume.

5. The photodiode assembly of claim 3, wherein the ground diffusion
region is disposed between the elongated doped regions around the
photodiode cell.

6. The photodiode assembly of claim 1, wherein the guard band includes
elongated doped regions of the substrate that extend around the
photodiode cell and around the ground diffusion region.

7. The photodiode assembly of claim 1, wherein the ground diffusion
region includes a plurality of spaced apart ground diffusion regions
disposed around the photodiode cells and an elongated ground diffusion
region that extends between and couples the spaced apart ground diffusion
regions.

8. The photodiode assembly of claim 1, wherein the photodiode cell and
the guard band include p-doped regions of the substrate.

9. The photodiode assembly of claim 1, further comprising an adjustable
voltage source conductively coupled with the guard band, the guard band
configured to receive a biasing voltage from the voltage source.

10. The photodiode assembly of claim 1, wherein the photodiode assembly
forms at least a part of a detector in a computed tomography imaging
system, a security system, or another imaging system.

11. A method for providing a photodiode assembly, the method comprising:
diffusing a first type of dopant into a first volume of a substrate to
form a photodiode cell; forming a ground diffusion region in the
substrate by diffusing a second type of dopant into the substrate, the
first and second types of dopants being oppositely charged dopants; and
forming a guard band in the substrate that at least partially extends
around an outer periphery of the photodiode cell, the guard band formed
by diffusing the first type of dopant into a collection region of the
substrate, the guard band disposed closer to the photodiode cell than the
ground diffusion region, wherein at least one of the ground diffusion
region or the guard band is conductively coupled with a ground reference
to conduct one or more of electrons or holes that drift from the
photodiode cell through the substrate.

12. The method of claim 11, wherein forming the guard band includes
diffusing the first type of dopant into a volume of the substrate that is
spaced apart from the photodiode cell by a separation portion of the
substrate that continuously extends from the photodiode cell to the
collection region.

13. The method of claim 12, wherein the separation portion of the
substrate extends between the photodiode cell and the guard band without
presence of the second type of dopant or a dopant junction.

14. The method of claim 11, further comprising conductively coupling the
guard band with an adjustable voltage source, the guard band configured
to receive a biasing voltage from the voltage source.

15. The method of claim 11, wherein forming the guard band includes
diffusing the first type of dopant into volumes of the substrate that
include elongated doped regions of the substrate oriented at non-parallel
angles with respect to each other and diffusing the second type of dopant
into the ground diffusion region that includes joint regions of the
substrate that are joined with the elongated doped regions.

16. A photodiode assembly comprising: a semiconductor substrate; an array
of photodiode cells disposed in the substrate, the photodiode cells
including spaced apart volumes of the substrate that are doped with a
first type of dopant; and guard bands disposed in the substrate between
the photodiode cells, the guard bands including commonly doped volumes of
the substrate that are doped with the first type of dopant; ground
diffusion regions disposed in the substrate farther from the photodiode
cells than the guard bands, the ground diffusion regions doped with a
different, second type of dopant than the first type of dopant, wherein
the guard bands are configured to conduct at least one of electrons or
holes drifting through the substrate from the photodiode cells to a
ground reference and the ground diffusion regions are configured to
conduct the other of electrons or holes drifting through the substrate
from the photodiode cells to the ground reference.

17. The photodiode assembly of claim 16, wherein the guard bands are
separated from the photodiode cells by separation portions of the
substrate that continuously extend from the photodiode cells to the guard
bands, the separation portions not including regions doped with the
second type of dopant.

18. The photodiode assembly of claim 16, wherein the guard bands include
elongated doped regions of the substrate that extend around the
photodiode cells and around the ground diffusion regions.

19. The photodiode assembly of claim 16, wherein the ground diffusion
regions include a plurality of spaced apart ground diffusion regions
disposed around the photodiode cells and one or more elongated ground
diffusion regions that extend between and couple the spaced apart ground
diffusion regions.

20. The photodiode assembly of claim 16, wherein the guard bands are
conductively coupled with a voltage source, the guard band configured to
receive a biasing voltage from the voltage source.

Description:

BACKGROUND OF THE INVENTION

[0001] The subject matter described herein relates to semiconductor
devices, such as photodiodes and photosensors.

[0002] Some known imaging systems include photosensitive detectors that
receive incident radiation, such x-rays, to generate an image. The
radiation is received by photodiodes in the detector and is converted
into an electric charge or signal. The magnitude of the charge or signal
can represent the amount of attenuation of the incident radiation and be
used to generate an image.

[0003] In order to provide images with relatively high resolution, the
photodiodes in the detector may need to be positioned relatively close to
each other. The photodiodes can generate electrical signals that are not
representative of the radiation received by the individual photodiodes.
These signals are referred to as electrical crosstalk. The crosstalk can
drift through the photodiode array in the form of electrons and electron
holes (e.g., the absence of electrons at lattice points in the
semiconductor structure of a detector). The crosstalk may drift from one
cell of a photodiode array to another nearby cell within the same
photodiode array and alter the charge or signal generated by the
photodiode in response to receiving incident radiation. As a result, the
image generated by the photodiodes may be negatively impacted by the
crosstalk.

[0004] Some detectors include areas of a semiconductor substrate that are
heavily doped with n+ dopants, such as phosphorus (P), in order to make
the substrate more conductive. These areas attempt to prevent crosstalk
from drifting between cells of the photodiode array by conducting the
electrons of the crosstalk out of the photodiode array. However, the use
of n+ doped regions can reduce the amount of crosstalk that is removed
from the detector. For example, the n+ doped regions may reflect part of
the crosstalk, such as the electron holes of the crosstalk, back toward
the photodiode cells instead of conducting the electron holes out of the
detector. As a result, at least some of the crosstalk may continue to
drift to the photodiodes and degrade image quality.

BRIEF DESCRIPTION OF THE INVENTION

[0005] In one embodiment, a photodiode assembly is provided. The assembly
includes a semiconductor substrate, a photodiode cell, a ground diffusion
region, and a guard band. The photodiode cell in disposed the substrate
and includes a first volume of the substrate that is doped with a first
type of dopant. The ground diffusion region is disposed in the substrate
and includes a second volume of the substrate that is doped with a second
type of dopant having an opposite charge relative to the first type of
dopant. The guard band is disposed in the substrate and at least
partially extends around an outer periphery of the photodiode cell. The
guard band includes a third volume of the substrate that is doped with
the first type of dopant. At least one of the ground diffusion region or
the guard band is conductively coupled with a ground reference to conduct
one or more of electrons or holes that drift from the photodiode cell
through the substrate. The guard band is disposed closer to the
photodiode cell than the ground diffusion region.

[0006] In another embodiment, a method for providing a photodiode assembly
is provided. The method includes diffusing a first type of dopant into a
first volume of a substrate to form a photodiode cell and forming a
ground diffusion region in the substrate by diffusing a second type of
dopant into the substrate. The first and second types of dopants are
oppositely charged dopants. The method also includes forming a guard band
in the substrate that at least partially extends around an outer
periphery of the photodiode cell. The guard band is formed by diffusing
the first type of dopant into a collection region of the substrate and is
disposed closer to the photodiode cell than the ground diffusion region.
At least one of the ground diffusion region or the guard band is
conductively coupled with a ground reference to conduct one or more of
electrons or holes that drift from the photodiode cell through the
substrate.

[0007] In another embodiment, another photodiode assembly is provided. The
assembly includes a semiconductor substrate, an array of photodiode
cells, guard bands, and ground diffusion regions. The array of photodiode
cells is disposed in the substrate and includes spaced apart volumes of
the substrate that are doped with a first type of dopant. The guard bands
are disposed in the substrate between the photodiode cells and include
commonly doped volumes of the substrate that are doped with the first
type of dopant. The ground diffusion regions are disposed in the
substrate farther from the photodiode cells than the guard bands and are
doped with a different, second type of dopant than the first type of
dopant. The guard bands are configured to conduct at least one of
electrons or holes drifting through the substrate from the photodiode
cells to a ground reference and the ground diffusion regions are
configured to conduct the other of electrons or holes drifting through
the substrate from the photodiode cells to the ground reference.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The presently disclosed subject matter will be better understood
from reading the following description of non-limiting embodiments, with
reference to the attached drawings, wherein below:

[0009]FIG. 1 is a perspective view of one embodiment of a portion of a
photodiode assembly.

[0010]FIG. 2 is a cross-sectional view of the photodiode assembly shown
in FIG. 1.

[0011]FIG. 3 is a top view of another embodiment of a photodiode
assembly.

[0012]FIG. 4 is a cross-sectional view of the photodiode assembly along
line 4-4 in FIG. 3.

[0013]FIG. 5 is a top view of a photodiode assembly according to another
embodiment.

[0014]FIG. 6 is a cross-sectional view of the photodiode assembly along
line 6-6 in FIG. 5.

[0015]FIG. 7 is a top view of a photodiode assembly according to another
embodiment.

[0016]FIG. 8 is a cross-sectional view of the photodiode assembly along
line 8-8 in FIG. 8.

[0017]FIG. 9 is a top view of a photodiode assembly according to another
embodiment.

[0018]FIG. 10 is a cross-sectional view of the photodiode assembly along
line 10-10 in FIG. 9.

[0019]FIG. 11 is a flowchart of one embodiment for a method for providing
a photodiode assembly.

DETAILED DESCRIPTION

[0020] As used herein, an element or step recited in the singular and
proceeded with the word "a" or "an" should be understood as not excluding
plural of said elements or steps, unless such exclusion is explicitly
stated. Furthermore, references to "one embodiment" of the invention do
not exclude the existence of additional embodiments that also incorporate
the recited features. Unless explicitly stated to the contrary,
embodiments "comprising," "including," or "having" an element or a
plurality of elements having a particular property may include additional
such elements not having that property.

[0021] The subject matter described herein relates to photosensor
assemblies used in imaging systems. The photosensor assemblies may be
used to generate images based on incident radiation. For example, the
photosensor assemblies may be used with a computed tomography (CT) system
to convert incident radiation into an image. Alternatively, the
photosensor assemblies may be used with security systems to convert
incident radiation into an image or to detect the presence of a body,
such as that of an intruder. However, not all embodiments described
herein are limited to CT systems or security systems. Other systems or
apparatuses that convert radiation into electrical signals for forming
images or for other purposes may include one or more embodiments
described herein.

[0022] The photosensor assemblies include substrates having photodiode
cells disposed therein that convert the incident radiation into electric
signals or charges that are used to form the image. Dopants are diffused
into the substrates between the photodiode cells along the interior of
the substrate (e.g., not along the exterior boundary in one embodiment)
to form guard bands and ground diffusion regions. The guard bands and the
ground diffusion regions are provided in the photodiode assembly to
prevent or reduce electrons and/or holes generated in or near one
photodiode cell from drifting to another neighboring photodiode cell.
Such drift of electrons and/or holes may otherwise change the signal or
charge generated by the neighboring photodiode cell.

[0023] The guard bands may attract and/or accept the holes that drift from
the photodiode cells while the ground diffusion regions can repel the
holes toward the guard bands. The ground diffusion regions can attract
and/or accept the electrons the drift from the photodiode cells. The
guard bands and the ground diffusion regions may be conductively coupled
with each other and the ground diffusion regions may be conductively
coupled with an electric ground reference. For example, the guard bands
and the ground diffusion regions may be conductively coupled to a common
electrode or bus. The guard bands and ground diffusion regions conduct
the electrons and holes to the ground reference before the electrons and
holes reach a nearby or neighboring photodiode cell.

[0024] In one embodiment, the guard bands may include hole collection
regions of the substrate that are doped with the same dopant or same type
of dopant ("commonly doped regions) as the photodiode cells. The ground
diffusion regions may include electron collection regions of the
substrate that are doped with a different dopant or different type of
dopant ("differently doped regions"). For example, if the photodiode
cells are formed from p- or p+ doped regions of an n-doped semiconductor
substrate, then the ground diffusion regions may be formed from n or n+
doped regions of the semiconductor substrate that collects or accepts
electron holes, or the absence of an electron in the semiconductor
lattice of the substrate, that drift through the substrate as an
electrical component of crosstalk. The holes and/or electrons are
conducted through the guard bands and/or the ground diffusion regions to
the electric ground reference and prevented from drifting to another
photodiode cell.

[0025]FIG. 1 is a perspective view of one embodiment of a portion of a
photodiode assembly 100. FIG. 2 is a cross-sectional view of the
photodiode assembly 100 shown in FIG. 1. The photodiode assembly 100 is a
radiation detection device that can be used as an image detector, such as
a detector for a CT imaging system or a security system. For example, the
photodiode assembly 100 may receive incident radiation 102, such as
x-rays or light from a photoscintillator and attenuated x-rays used to
image a body, on a light entry side 104 of the photodiode assembly 100.
The photodiode assembly 100 includes an array 106 of photodiode cells
108. The photodiode cells 108 generate electrical signals or charges in
response to photons of the radiation 102 striking the photodiode assembly
100. The signals or charges may be read out or examined to generate an
image based on the strength or magnitude of the radiation 102 that is
incident on the photodiode assembly 100 at the various photodiode cells
108. For example, the photodiode cells 108 can be conductively coupled
with readout electrodes 200 (shown in FIG. 2) that are conductively
coupled with conductive busses 202 (shown in FIG. 2). The busses 202
convey the signals or charges to a computing device or processor that
generates an image based on the signals or charges.

[0026] The photodiode assembly 100 includes a semiconductor substrate 110
formed from one or more semiconductor materials. By way of example only,
the semiconductor materials of the substrate 110 may include silicon
(Si), germanium arsenide (GeAs), cadmium telluride (CdTe), cadmium zinc
telluride (CdZnTe or CZT), and the like. The substrate 110 may be an
intrinsic semiconductor material that is not doped with any charged
dopant, such as an acceptor or p-type dopant (for example, boron (B)), or
a donor or n-type dopant (for example, phosphorus (P)). Alternatively,
the substrate 110 may be doped with one of the oppositely charged p- or
n-type dopants.

[0027] The photodiode cells 108 may be formed by depositing and/or
diffusing (collectively referred to herein as "diffusing") one or more
dopants into the substrate 110 in the areas shown in FIG. 1. For example,
p- or n-type dopants may be diffused into the substrate 110 through a
back side 112 of the substrate 110 to form the photodiode cells 108.
Alternatively, the dopants may be diffused into the substrate 110 through
an opposite light entry side 104 of the substrate 110 to form the
photodiode cells 108. In one embodiment, the substrate 110 is doped with
an n-type dopant, such as phosphorus (P), and the photodiode cells 108
are formed by diffusing an oppositely charged p-type dopant, such as
boron (B), into the substrate 110. Alternatively, the photodiode cells
108 may be formed by etching the substrate 110 to form voids and filling
the voids with doped semiconductor material to form the photodiode cells
108. The diffusion of the dopants into the substrate 110 forms dopant
junctions, such as p/n dopant junctions (for example, when a p-type
dopant is diffused into an n-doped substrate 110) and/or n/p dopant
junctions (for example, when an n-type dopant is diffused into a p-doped
substrate 110).

[0028] The dopants may be diffused in a variety of depths into the
substrate 110 to form the photodiode cells 108. By way of example only,
the dopants may be diffused to a depth of between approximately 0.05
micrometers and approximately 50 micrometers into the substrate 110 from
the back side 112 of the substrate 110. The photodiode cells 108 are
shown as square shapes. Alternatively, the photodiode cells 108 may have
a different shape, such as a hexagon, octagon, triangle, circle,
ellipsis, parallelogram, among other shapes.

[0029] The photodiode assembly 100 includes guard bands 114 at least
partially extend around the outer periphery of the photodiode cells 108.
For example, as shown in FIG. 1, the guard bands 114 may be arranged in a
regularly spaced grid and disposed between neighboring photodiode cells
108 along orthogonal or perpendicular directions. The guard bands 114 can
be formed by diffusing a dopant, such as a p- or n-type dopant, into the
substrate 110. Alternatively, the guard bands 114 may be formed by
etching trenches in the substrate 110 and depositing a doped
semiconductor in the substrate 110. In one embodiment, the guard bands
114 are formed by diffusing the same type of dopant from which the
photodiode cells 108 are formed. For example, in an n-doped substrate
110, the photodiode cells 108 and the guard bands 114 are formed by
diffusing a p-type dopant into the substrate 110. Diffusing the dopants
to form the guard bands 114 creates dopant junctions in the substrate
110, such as p/n and/or n/p dopant junctions. The dopants may be diffused
in a variety of depths into the substrate 110 to form the guard bands
114. By way of example only, the dopants may be diffused to a depth of
between approximately 0.20 micrometers and approximately 50 micrometers
into the substrate 110 from the film side 112 of the substrate 110.

[0030] The guard bands 114 reduce the amount of electrical crosstalk that
is conducted, or drifts, between neighboring photodiode cells 108 (e.g.,
adjacent cells). In one embodiment, the guard bands 114 are conductively
coupled with a signal ground reference 116. For example, the guard bands
114 may be joined to one or more conductive ground electrodes 118 that
are conductively coupled with the signal ground reference 116. Electrical
crosstalk that reaches the guard bands 114 is conveyed to the ground
reference so that the crosstalk is not conducted to the neighboring
photodiode cells 108. For example, electrons and/or holes in the
semiconductor material of the photodiode cells 108 that are not read out
as an image signal from the photodiode cells 108 may drift through the
substrate 110 out of the photodiode cells 108. The electrons and/or holes
may continue to move through the lattice structure of the substrate 110
until the electrons and/or holes reach the guard bands 114 and are
conducted to the ground reference 116.

[0031] Alternatively, one or more of the guard bands 114 may be
conductively coupled with an adjustable voltage source 120, such as a
battery, direct current source, or other source of current, that applies
an adjustable biasing voltage to the guard bands 114. The biasing voltage
can be manually or automatically varied or changed. The biasing voltage
can be applied to the guard bands 114 to offset or eliminate the
electrons and/or holes that drift from the photodiode cells 108 to the
guard bands 114. For example, the biasing voltage may change the
effective charge or electric potential of the guard bands 114. Changing
the effective charge or potential of the guard bands 114 may alter the
effective depth and/or width of the guard bands 114. For example,
applying a negative potential or voltage to the guard bands 114 may cause
the guard bands 114 to attract less holes and thereby effectively
decrease the effective depth and/or width of the guard bands 114.
Conversely, applying a positive potential or voltage to the guard bands
114 may cause the guard bands 114 to attract more holes and thereby
increase the effective depth and/or width of the guard bands 114. For
example, if the electrical crosstalk generated by the photodiode cells
108 is approximately +10 millivolts, then an offset biasing voltage of
approximately -10 millivolts may be supplied to the guard bands 114 by
the voltage source 120 to offset and/or neutralize the electrical
crosstalk that reaches the guard bands 114.

[0032] In one embodiment, the photodiode assembly 100 includes a backside
passivation layer 122 on the incident side 104 of the substrate 110. The
passivation layer 122 is a layer that chemically and/or electrically
passivates the substrate 110. For example, the passivation layer 122 may
be diffused onto the substrate 110 to prevent contaminants from diffusing
into the substrate 110 through the incident side 104, to prevent chemical
reactions between the substrate 110 and other chemical species at the
incident side 104, and/or to prevent conductive contact between the
incident side 104 and another body. The passivation layer 122 may be
diffused as a layer of silicon dioxide (SiO2) and/or silicon nitride
(Si3N4), or another chemically and/or electrically passivating
substance. The passivation layer 122 also may enhance photon transmission
for collection of photons in the photodiode cells 108. The thickness of
the passivation layer 122 may be approximately 0.01 micrometers to
approximately 5 micrometers. Alternatively, a smaller or larger thickness
may be used. Combinations of silicon dioxide and silicon nitride also may
be used.

[0033] FIGS. 3 through 10 illustrate bottom and cross-sectional views of
several embodiments of a photodiode assembly. The embodiments shown in
FIGS. 3 through 10 may operate similar to the photodiode assembly 100
shown in FIGS. 1 and 2. For example, the photosensor assemblies include
photodiode cells that convert incident radiation into electric signals or
charges which are read out to generate an image. The photosensor
assemblies include guard bands and ground diffusion regions that reduce
or eliminate drift of electrons and/or holes between neighboring
photodiode cells. The photosensor assemblies may include a greater number
of photodiodes, guard bands, and/or ground diffusion regions than what is
shown in the Figures.

[0034]FIG. 3 is a top view of one embodiment of a portion of a photodiode
assembly 300. FIG. 4 is a cross-sectional view of the portion of the
photodiode assembly 300 along line 4-4 in FIG. 3. The photodiode assembly
300 includes a semiconductor substrate 302, such as a p-doped, n-doped,
or intrinsic silicon (Si) substrate. In one embodiment, the substrate 302
is an n-doped semiconductor substrate. Alternatively, the substrate 302
may be formed from another semiconductive material.

[0035] The substrate 302 includes photodiode cells 304 that convert
incident radiation into electric signals or charges. The photodiode cells
304 may be arranged in a regularly spaced array of photodiode cells 304.
The photodiode cells 304 include, or are formed from, doped volumes 306
of the substrate 302. In one embodiment, the volumes 306 of the substrate
302 may be doped to form a dopant junction in the substrate 302, with the
dopant junctions forming the photodiode cells 304. In one embodiment, the
photodiode cells 304 are formed by diffusing a p-type dopant, such as
boron (B), into the volumes 306 of the substrate 302 to form a p/n
junction. In another embodiment, the photodiode cells 304 are formed by
diffusing another acceptor or p-type dopant into the substrate 302.
Alternatively, the photodiode cells 304 may be formed by removing the
volumes 306 from the substrate 302 (such as by etching) and depositing a
doped semiconductor into the volumes 306. In another embodiment, the
photodiode cells 304 are formed by diffusing an n-type dopant into the
substrate 302.

[0036] Although not shown in FIG. 4, the photodiode cells 304 may be
conductively coupled with readout busses similar to the photodiode cells
108 (shown in FIG. 1) to permit the signals or charges generated by the
photodiode cells 304 to be obtained and used to generate an image. The
photodiode cells 304 can be positioned relatively close to each other to
increase the resolution of images that are obtained using the photodiode
assembly 300. A separation distance 320 can represent the spatial
separation of the photodiode cells 304 from each other. In one
embodiment, the separation distance 320 between neighboring photodiode
cells 304 is no greater than 250 micrometers, or 9.8 mils. In another
embodiment, the separation distance 320 is no greater than 150
micrometers, or 5.9 mils. Alternatively, the separation distance 320 is
no greater than 30 micrometers, or 1.2 mils. Other separation distances
320 are likewise contemplated.

[0037] The photodiode assembly 300 includes elongated guard bands 308 that
at least partially extend around the outer peripheries of the individual
photodiode cells 304. The guard bands 308 include commonly doped
collection regions 312, 314. As used herein, the term "commonly doped" is
used to identify portions or volumes of the substrate that are doped with
the same type of dopants or the same dopants as the photodiode cells. By
way of example, if the photodiode cells 304 are formed by doping volumes
of the substrate 302 with a p-type or acceptor dopant, such as boron (B),
then other volumes of the substrate 302 that are doped with boron (B) or
with another p-type or acceptor dopant may be referred to as commonly
doped volumes or regions. On the other hand, volumes of the substrate
that are doped with phosphorus (P) or with another n-type or donor dopant
may be referred to as differently doped volumes or regions. In accordance
with one embodiment, the guard bands include commonly doped regions of
the substrate.

[0038] The collection regions 312 may be referred to as horizontal regions
and the collection regions 314 may be referred to as vertical regions.
Additionally, as used herein, the terms "horizontal" and "vertical"
merely denote the orientation of different diffused regions in a
substrate and are not intended to limit all embodiments of the disclosed
subject matter. For example, the collection regions 312, 314 may be
oriented in other directions. While the collection regions 312, 314 are
perpendicularly oriented with respect to each other in the illustrated
embodiment, alternatively, the collection regions 312, 314 may be
obliquely oriented with respect to each other (e.g., oriented at an angle
other than ninety degrees). For example, the collection regions 312, 314
may be oriented in transverse, or non-parallel, angles with respect to
each other.

[0039] In the illustrated embodiment, the commonly doped collection
regions 312, 314 are separated from each other. The vertical collection
regions 314 are disposed between neighboring photodiode cells 304 along a
first direction 326 and the horizontal collection regions 312 are
disposed between neighboring photodiode cells 304 along a second,
orthogonal or perpendicular direction 328 in the illustrated embodiment.
As shown in FIG. 3, the collection regions 312, 314 are spaced apart such
that the collection regions 312, 314 are not directly coupled with each
other (e.g., the regions 312, 314 do not abut each other).

[0040] The collection regions 312, 314 of the guard bands 308 include, or
are formed from, doped volumes 310 of the substrate 302. The volumes 310
of the substrate 302 are doped with an n- or p-type dopant to form a
dopant junction in the substrate 302, with the dopant junctions forming
the collection regions 312, 314. In one embodiment, the individual and
separate segments of the guard bands 308 that form the collection regions
312, 314 are created by diffusing the same type of dopant as the
photodiode cells 304. For example, the photodiode cells 304, the
horizontal collection segments 312, and the vertical collection segments
314 may be formed by diffusing a p-type dopant, such as boron (B), into
the volumes 306 and the volumes 310 of the substrate 302. Alternatively,
the collection segments 312, 314 may be formed by removing the volumes
310 from the substrate 302 (such as by etching) and diffusing a doped
semiconductor into the volumes 310.

[0041] In the illustrated embodiment, ground diffusion regions 318 are
disposed at or near the corners of the photodiode cells 304. For example,
the ground diffusion regions 318 may be disposed between neighboring
photodiode cells 304 along directions that are obliquely angled with
respect to the directions 326, 328. In the embodiment shown in FIG. 3
where the guard bands 308 have a square shape, the ground diffusion
regions 318 may be located at the corners of the square shapes
approximately formed by the guard bands 308 with the collection regions
312, 314 forming the sides of the square guard bands 308. Alternatively,
the guard bands 308 may have a different shape, such as a hexagon,
octagon, triangle, circle, ellipsis, parallelogram, and the like.

[0042] The ground diffusion regions 318 include, or are formed from,
volumes of the substrate 302 that are doped with an n- or p-type dopant.
In one embodiment, the ground diffusion regions 318 represent doped
volumes of the substrate 302 that form a dopant junction in the substrate
302. The ground diffusion regions 318 may be formed using an oppositely
charged dopant as the photodiode cells 304 and/or the collection regions
312, 314. For example, the ground diffusion regions 318 may be formed
from n-doped volumes of the substrate 302 while the photodiode cells 304
and the collection regions 312, 314 are formed from p-doped volumes of
the substrate 302.

[0043] Similar to the guard bands 114 (shown in FIG. 1), the guard bands
308 may be conductively coupled with a ground reference similar to the
guard bands 114 (shown in FIG. 1). For example, the ground diffusion
regions 318 may be coupled with the signal ground reference and the
collection regions 312, 314 may be joined with the ground diffusion
regions 318. Alternatively, both the ground diffusion regions 318 and the
collection regions 312, 314 may be joined to a common conductive ground
electrode. The collection regions 312, 314 may be coupled with the ground
diffusion regions 318 by diffusing the collection regions 312, 314 and
ground diffusion regions 318 adjacent to each other. Alternatively or
additionally, conductive bodies or busses may be provided that contacts
the collection regions 312, 314 with the diffusion regions 318 by
metalizing a connection between the regions 312, 314, 318.

[0044] Electrical crosstalk (e.g., electrons and/or holes) may be
generated by the photodiode cells 304. The holes of the crosstalk may
drift to the collection regions 312, 314 and/or the ground diffusion
regions 318. The holes are attracted to the collection regions 312, 314
but are repelled by the ground diffusion regions 318 in one embodiment.
The repulsion by the ground diffusion regions 318 may direct at least
some of the holes toward the collection regions. The electrons of the
crosstalk may drift to the ground diffusion regions 318. The holes are
conducted to the ground reference by being conducted through the
collection regions 312, 314 to the ground diffusion regions 318, and then
to the electric ground reference. The electrons are conducted to the
ground reference by being conducted through the ground diffusion regions
318 to the ground reference.

[0045] In the illustrated embodiment, the substrate 302 extends between
and separates the guard bands 308 from the photodiode cells 304, without
any other diffused regions or junctions disposed between the photodiode
cells 304 and the guard bands 308. For example, the substrate 302 may
continuously extend from outer peripheries of a photodiode cell 304 to
the collection regions 312, 314 of the guard bands 308 disposed between
the photodiode cell 304 and neighboring photodiode cells 304. By
"continuously extend," the substrate 302 may be disposed between the
photodiode cells 304 and the guard bands 308 such that no doped regions,
dopant junctions, and/or etched volumes are located in the substrate 302
between the photodiode cells 304 and the guard bands 308 that separate
the photodiode cells 304 from neighboring photodiode cells 304. The
substrate 302 may extend, without interruption or inclusion of additional
doped volumes, from the photodiode cells 304 to the guard bands 308. The
volumes or sections of the substrate 302 that separate and extend from
the photodiode cells 304 to the guard bands 308 may be referred to as
separation regions 316 of the substrate 302. Electrical crosstalk may
pass through the separation regions 316 from the photodiode cells 304 to
the guard bands 308 and be conducted to the signal ground reference by
the guard bands 308.

[0046] The width of the guard bands 308 can be varied to change the how
much of the crosstalk signals generated by the photodiode cells 304 are
captured by the guard bands 308 and conducted to the signal ground
reference. For example, a width dimension 322 may represent the lateral
width or size of the horizontal and/or vertical collection regions 312,
314 of the guard bands 308 at a film side 324 of the substrate 302.
Increasing the width dimension 322 may allow the guard bands 308 to
capture larger crosstalk signals (e.g., crosstalk signals having larger
amounts of energy) relative to smaller width dimensions 322. In one
embodiment, the width dimension 322 is no greater than 100 micrometers,
or 3.9 mils. In another embodiment, the width dimension 322 is no greater
than 50 micrometers, or 2.0 mils. Alternatively, the width dimension 322
is no greater than 1 micrometer, or 0.04 mils. The sizes of the ground
diffusion regions 318 similarly may be adjusted to vary the magnitude of
crosstalk signals that is conducted to the signal ground reference.

[0047]FIG. 5 is a top view of a portion of a photodiode assembly 500
according to another embodiment. FIG. 6 is a cross-sectional view of the
photodiode assembly 500 along line 6-6 in FIG. 5. Similar to the
photodiode assembly 100 (shown in FIG. 1), the photodiode assembly 500
includes a semiconductor substrate 502, such as a p-doped, n-doped, or
intrinsic semiconductor substrate. In one embodiment, the substrate 502
is an n-doped silicon (Si) substrate.

[0048] The substrate 502 includes photodiode cells 504 that include, or
are formed from, volumes 506 of the substrate 502 that are doped with an
n- or p-type dopant. In one embodiment, the photodiode cells 504 are
formed from p-doped volumes 506 of the substrate 502. The photodiode
cells 504 may be conductively coupled with readout busses similar to the
photodiode cells 108 (shown in FIG. 1) to permit the signals or charges
generated by the photodiode cells 504 to be obtained and used to generate
an image.

[0049] The photodiode assembly 500 includes encircling guard bands 508
that at least partially extend around the outer peripheries of the
individual photodiode cells 504. In the illustrated embodiment, the guard
bands 508 continuously extend around the outer peripheries of the
photodiode cells 504. The guard bands 508 include commonly doped volumes
of the substrate 502 in one embodiment. For example, the guard bands 508
may include, or be formed from, volumes 510 of the substrate 502 that are
doped with the same dopant or same type of dopant as the photodiode cells
504. The commonly doped volumes may be referred to as collection regions.

[0050] The guard bands 508 may surround the photodiode cells 504 such that
the guard bands 508 are disposed between neighboring photodiode cells
504. In the illustrated embodiment, the guard bands 508 include commonly
doped collection regions 512 and commonly doped interconnecting regions
516. The collection regions 512, 514 include horizontal and vertical
collection regions 512, 514 that may be formed from the same type of
dopant used to create the photodiode cells 504. For example, the
photodiode cells 504 and the collection regions 512, 514 may be formed by
diffusing a p-type dopant, such as boron (B), into the substrate 502
while the ground diffusion regions 518 are formed by diffusing an n-type
dopant, such as phosphorus (P), into the substrate 502.

[0051] The substrate 502 includes ground diffusion regions 518 that
include volumes of the substrate 502 that are doped with a different or
oppositely charged dopant relative to the dopant(s) used to create the
photodiode cells 504 and/or the collection and interconnecting regions
512, 514, 516. For example, the ground diffusion regions 518 may be
formed by diffusing an n-type dopant (such as phosphorus) into the
substrate 502. The ground diffusion regions 518 may be conductively
coupled with an electric ground reference. For example, one or more
conductive ground electrodes may conductively couple the ground diffusion
regions 518 with a ground reference.

[0052] In contrast to the photodiode assembly 300 (shown in FIG. 3), the
collection regions 512, 514 of the guard bands 508 are coupled with each
other. For example, the collection regions 512, 514 are coupled with each
other by the interconnecting regions 516 of the guard bands 508 such that
the collection regions 512, 514 and interconnecting regions 516 form a
continuous body that encircles the photodiode cell 504. The
interconnecting regions 516 may be extensions of the horizontal and/or
vertical collection regions 512, 514 that join the horizontal and
vertical collection regions 512, 514. As shown in FIG. 5, the
interconnecting regions 516 couple the collection regions 512, 514 such
that the horizontal, vertical, and interconnecting regions 512, 514, 516
entirely encircle the ground diffusion regions 518 (as shown in FIG. 5)
in one embodiment.

[0053] Similar to the photodiode assembly 300 shown in FIG. 3, the
substrate 502 extends between and separates the guard bands 508 from the
photodiode cells 504. The substrate 502 may continuously extend from
outer peripheries of a photodiode cell 504 to the collection and
interconnecting regions 512, 514, 516 of the guard bands 508 that at
least partially surround the photodiode cell 504 and separate the
photodiode cell 504 from neighboring photodiode cells 504.

[0054] Also similar to the photodiode assembly 300 (shown in FIG. 3), the
ground diffusion regions 518 may be conductively coupled with the signal
ground reference. The interconnecting regions 516 may abut or overlap the
ground diffusion regions 518 such that the interfaces between the ground
diffusion regions 518 and the interconnecting regions 518 form a dopant
junction. Electrical crosstalk signals from the photodiode cells 504 may
be conducted through the substrate 502 to the horizontal and/or vertical
collection regions 512, 514. The collection regions 512, 514 may be doped
so as to be more conductive than the substrate 502. As a result, the
crosstalk signals in the collection regions 512, 514 may be conducted to
the ground diffusion regions 518 via the interconnecting regions 516. The
ground diffusion regions 518 may then conduct the crosstalk signals to
the ground reference.

[0055]FIG. 7 is a top view of a portion of a photodiode assembly 700
according to another embodiment. FIG. 8 is a cross-sectional view of the
photodiode assembly 700 along line 8-8 in FIG. 8. Similar to the
photodiode assembly 100 (shown in FIG. 1), the photodiode assembly 700
includes a semiconductor substrate 702, such as a p-doped, n-doped, or
intrinsic semiconductor substrate. In one embodiment, the substrate 702
is an n-doped silicon (Si) substrate.

[0056] The substrate 702 includes photodiode cells 704 that include, or
are formed from, volumes 706 of the substrate 702 that are doped with an
n- or p-type dopant. In one embodiment, the photodiode cells 704 are
formed from p-doped volumes 706 of the substrate 702. The photodiode
cells 704 may be conductively coupled with readout busses similar to the
photodiode cells 108 (shown in FIG. 1) to permit the signals or charges
generated by the photodiode cells 704 to be obtained and used to generate
an image.

[0057] The photodiode assembly 700 includes individual cell guard bands
708 that at least partially extend around the outer peripheries of the
individual photodiode cells 704. Similar to the guard bands 108, 308, 508
(shown in FIGS. 1, 3, and 5), the guard bands 708 separate individual
photodiode cells 704 from each other. In the illustrated embodiment, the
guard bands 708 include elongated commonly doped collection regions 712,
714. The collection regions 712, 714 include horizontal collection
regions 712 and vertical collection regions 714. As described above, the
commonly doped collection regions 712 714 can be formed by diffusing the
same type or charged dopant as the dopant that is used to form the
photodiode cells 704 (e.g., a p-dopant).

[0058] The photodiode assembly 700 also includes elongated interior ground
diffusion regions 716 and ground diffusion regions 718. The ground
diffusion regions 716, 718 include volumes of the substrate 702 that are
doped with a different type or oppositely charged dopant relative to the
dopant(s) used to form the collection regions 712, 714 and/or the
photodiode cells 704. For example, the ground diffusion regions 716, 718
may be formed as n-doped volumes of the substrate 702. In one embodiment,
the ground diffusion regions 716, 718 are collectively coupled with the
signal ground reference of the assembly 700. As shown in FIG. 7, the
elongated interior ground diffusion regions 716 interconnect the ground
diffusion regions 718 such that the ground diffusion regions 716, 718
encircle each of the photodiode cells 704 shown in FIG. 7.

[0059] The collection regions 712, 714 are disposed on opposite sides of
the interconnecting regions 716. For example, the interconnecting regions
716 may be disposed between the horizontal collection regions 712 in a
pair of horizontal collection regions 712 and between the vertical
collection regions 714 in a pair of vertical collection regions 714. As
shown in FIG. 7, each pair of horizontal collection regions 712 and each
pair of vertical collection regions 714 includes one horizontal or
vertical collection region 712, 714 disposed closer to the photodiode
cell 704 than the interconnecting regions 716 and one horizontal or
vertical collection region 712, 714 disposed farther from the photodiode
cell 704 than the interconnecting regions 716.

[0060] The ground diffusion regions 718 are spaced apart from each other
along the outer periphery of each photodiode cell 704 in the illustrated
embodiment. The interconnecting regions 716 may extend between and couple
the ground diffusion regions 718 that extend around the photodiode cell
704. The interior collection regions 712, 714 can extend between and
couple the neighboring ground diffusion regions 718. In the illustrated
embodiment, the interior collection regions 712, 714 are not joined with
each other. Alternatively, the ground diffusion regions 718 may be
de-coupled or spatially separated from one or more of the interconnecting
regions 716, horizontal collection regions 712, and/or vertical
collection regions 714. As shown in FIG. 7, the ground diffusion regions
718 and interconnecting regions 716 at least partially encircle the
photodiode cells 704 and the interior collection regions 712, 714. For
example, the interior collection regions 712, 714 are disposed between
the interconnecting regions 716 and the photodiode cell 704.

[0061] The substrate 702 may continuously extend between and separate the
horizontal and vertical collection regions 712, 714 of the guard bands
708 from the photodiode cells 704. For example, the substrate 702 may
continuously extend from outer peripheries of a photodiode cell 704 to
the interior collection regions 712, 714 without any other doped regions
or junctions disposed within the substrate 702 therebetween. The interior
collection regions 712, 714 are spaced apart from the interconnecting
regions 716. For example, the substrate 702 may continuously extend
between and separate the horizontal collection regions 712 from the
interconnecting regions 716 and between the vertical collection regions
714 from the interconnecting regions 716.

[0062] The ground diffusion regions 718 may be conductively coupled with a
signal ground reference to conduct electrons drifting from the photodiode
cells 704 to the signal ground reference. The guard bands 708 may be
coupled with the ground diffusion regions 718. As a result, holes that
drift from the photodiode cells 704 may drift to and be collected in the
horizontal and vertical collection regions 712, 714. Crosstalk signals
from the photodiode cells 704 may be conducted through the substrate 702
to the interior horizontal and/or vertical collection regions 712, 714.
The crosstalk signals in the interior collection regions 712, 714 may be
conducted to the signal ground reference via the ground diffusion regions
718. Alternatively, at least some of the crosstalk signals may be
conducted from the horizontal and/or vertical collection regions 712, 714
to the interconnecting regions 716, and from the interconnecting regions
716 to the signal ground reference through the ground diffusion regions
718.

[0063]FIG. 9 is a top view of a portion of a photodiode assembly 900
according to another embodiment. FIG. 10 is a cross-sectional view of the
photodiode assembly 900 along line 10-10 in FIG. 9. Similar to the
photodiode assembly 100 (shown in FIG. 1), the photodiode assembly 900
includes a semiconductor substrate 902, such as a p-doped, n-doped, or
intrinsic semiconductor substrate. In one embodiment, the substrate 902
is an n-doped silicon (Si) substrate.

[0064] The substrate 902 includes photodiode cells 904 that include, or
are formed from, volumes 906 of the substrate 902 that are doped with an
n- or p-type dopant. In one embodiment, the photodiode cells 904 are
formed from p-doped volumes 906 of the substrate 902. The photodiode
cells 904 may be conductively coupled with readout busses similar to the
photodiode cells 108 (shown in FIG. 1) to permit the signals or charges
generated by the photodiode cells 904 to be obtained and used to generate
an image.

[0065] The photodiode assembly 900 includes concentric guard bands 908
that at least partially extend around the outer peripheries of the
individual photodiode cells 904. Similar to the guard bands 108, 308,
508, 708 (shown in FIGS. 1, 3, 5, and 7), the guard bands 908 separate
individual photodiode cells 904 from each other. In the illustrated
embodiment, the guard bands 908 include a commonly doped interior
collection region 912 that encircles the photodiode cell 904. A
differently doped ground diffusion region 914 encircles the interior
collection region 912. Alternatively, the interior collection region 912
may include a separation, gap, or break such that the interior collection
region 912 does not entirely encircle the photodiode cell 904 and/or the
ground diffusion region 914 may include a separation, gap, or break such
that the ground diffusion region 914 does not entirely encircle the
interior collection region 912.

[0066] The interior collection regions 912 may be formed from the same
type of dopant used to create the photodiode cells 904 (e.g., a p-type
dopant) while the ground diffusion regions 914 may be formed from the
opposite dopant (e.g., an n-type dopant). As described above, one or more
of the regions 912, 914 may be formed by diffusing dopants into volumes
of the substrate 902 and/or by etching the substrate 902 and diffusing a
doped semiconductor into the substrate 902.

[0067] The interior collection regions 912 are spaced apart from the
diffusion band regions 914 by the substrate 902 in the illustrated
embodiment. For example, the substrate 902 may continuously extend
between and separate the interior collection regions 912 from the
diffusion band regions 914. Alternatively, one or more of the interior
collection regions 912 may abut or contact one or more of the diffusion
band regions 914. The substrate 902 can continuously extend between and
separate the guard bands 908 from the photodiode cells 904. For example,
the substrate 902 may continuously extend from outer peripheries of a
photodiode cell 904 to the interior collection region 912 of the guard
band 908 with no dopant diffused regions or dopant junctions in the
substrate 902 between the photodiode cells 904 and the collection regions
912.

[0068] The collection regions 912 and the ground diffusion regions 914 may
be conductively coupled with a ground reference to conduct electrons
and/or holes that drift from the photodiode cells 904 to the ground
reference in one embodiment. For example, the ground diffusion band
regions 914 may be conductively coupled with an electrode that is coupled
with a signal ground reference. The collection regions 912 may be joined
with the ground diffusion band regions 914 and/or be conductively coupled
with the same electrode that couples the ground diffusion band regions
914 to the ground reference. The holes that drift out of the photodiode
cells 904 may be collected by the collection regions 912 and conveyed to
the ground reference. The electrons that drift out of the photodiode
cells 904 may be collected by the ground diffusion regions 914 and
conducted to the ground reference.

[0069]FIG. 11 is a flowchart of one embodiment for a method 1100 for
providing a photodiode assembly. The method 1100 may be used to fabricate
one or more of the photosensor assemblies 100, 300, 500, 700, 900 (shown
in FIGS. 1, 3, 5, 7, and 9) described above. At 1102, a substrate is
provided. For example, a semiconductor substrate such as one or more of
the substrate 110, 302, 502, 702, 902 (shown in FIGS. 1, 3, 5, 7, and 9)
may be provided.

[0070] At 1104, a first dopant is diffused into the substrate to form one
or more photodiode cells. For example, a p-type dopant such as boron (B)
may be diffused into the substrate to form photodiode cells. The
photodiode cells may be arranged in a regularly spaced grid or array.

[0071] At 1106, the first dopant is diffused into the substrate to form a
first part of a guard band. For example, the first dopant or a dopant of
the same charge type as the dopant that was used to form the photodiode
cells is diffused into the substrate in one or more locations that are
spaced apart from the photodiode cells to form collection regions. The
first dopant is diffused into the locations that are spaced apart from
the photodiode cells to form a first part of the guard band. The
photodiode cells and the first part of the guard band may be formed
concurrently by masking the substrate and diffusing the first type of
dopant into different areas that correspond with the photodiode cells and
the first part of the guard band.

[0072] At 1108, a second, oppositely charged dopant is diffused into the
substrate to form a ground diffusion region of the substrate. For
example, a second dopant that has a charge that is opposite of the charge
of the first dopant is diffused into the substrate. The second dopant can
be an n-type dopant, such as phosphorus (P). The second dopant is
diffused in locations of the substrate that are located farther from the
photodiode cells than the parts of the guard band that are formed from
the first dopant in one embodiment.

[0073] At 1110, the photodiode cells are conductively coupled with readout
electrodes. For example, the photodiode cells may be coupled to
electrodes that are conductively coupled with readout electronics. The
readout electronics can determine the size or magnitude of the electrical
charged that are formed by the photodiode cells when incident radiation
strikes the photodiode cells to create an image, as described above.

[0074] At 1112, the guard band and the ground diffusion region are
conductively coupled with a ground reference. For example, one or more
electrodes may be coupled to the guard band and/or the collection
regions. The electrodes can be joined with the ground reference within
the semiconductor substrate. The electrodes are conductive coupled with
the signal ground reference in order to convey electrical crosstalk from
the photodiode cells to the ground reference. For example, the guard band
may be disposed between the photodiode cells such that electrical
crosstalk that drifts from the photodiode cells is conducted to the
ground reference by the guard band before the electrical crosstalk
reaches a neighboring photodiode cell.

[0075] In accordance with one or more embodiments, a method for providing
a photodiode assembly is disclosed. The method may be used to fabricate
one or more of the photosensor assemblies 100, 300, 500, 700, 900
disclosed herein and shown in FIGS. 1 through 10. The method includes
providing a substrate that may be doped with a p- or n-type dopant. The
photodiode cells are formed in the substrate by diffusing a dopant into
the substrate. The dopant used to form the photodiode cells may be an
oppositely charged dopant relative to the dopant in the substrate. For
example, a p-type dopant may be used to diffuse the photodiode cells when
the substrate is doped with an n-type dopant.

[0076] The method also includes forming guard bands around the photodiode
cells in the substrate. The guard bands separate individual photodiode
cells from each other. The guard bands may be provided by diffusing two
or more different types of dopants into the substrate. In one embodiment,
the guard bands are provided by forming both commonly doped and
differently doped regions in the substrate between neighboring photodiode
cells. For example, the guard bands may be provided by diffusing volumes
of the substrate with different dopants or different types of dopants
than the photodiode cells and by diffusing volumes of the substrate
between the differently doped regions and the photodiode cells with
commonly doped regions. As shown in FIGS. 1-10, various arrangements and
patterns of the photodiode cells and guard bands may be used.

[0077] The guard bands prevent, inhibit, or significantly reduce crosstalk
signals from one photodiode cell from drifting to a neighboring
photodiode cell. The differently doped volumes of the guard bands can be
conductively coupled with a signal ground reference. The commonly doped
volumes of the guard bands are located between the photodiode cells and
the differently doped volumes. The commonly doped volumes can collect
crosstalk signals generated by the photodiode cells. The crosstalk
signals may be conveyed from the commonly doped volumes to the
differently doped volumes, where the crosstalk signals are conducted to
the signal ground reference.

[0078] It is to be understood that the above description is intended to be
illustrative, and not restrictive. For example, the above-described
embodiments (and/or aspects thereof) may be used in combination with each
other. In addition, many modifications may be made to adapt a particular
situation or material to the teachings of the subject matter disclosed
herein without departing from its scope. While the dimensions and types
of materials described herein are intended to define the parameters of
the one or more embodiments of the subject matter, they are by no means
limiting and are exemplary embodiments. Many other embodiments will be
apparent to one of ordinary skill in the art upon reviewing the above
description. The scope of the subject matter described herein should,
therefore, be determined with reference to the appended claims, along
with the full scope of equivalents to which such claims are entitled. In
the appended claims, the terms "including" and "in which" are used as the
plain-English equivalents of the respective terms "comprising" and
"wherein." Moreover, in the following claims, the terms "first,"
"second," and "third," etc. are used merely as labels, and are not
intended to impose numerical requirements on their objects. Further, the
limitations of the following claims are not written in
means-plus-function format and are not intended to be interpreted based
on 35 U.S.C. §112, sixth paragraph, unless and until such claim
limitations expressly use the phrase "means for" followed by a statement
of function void of further structure.

[0079] This written description uses examples to disclose several
embodiments of the described subject matter, including the best mode, and
also to enable one of ordinary skill in the art to practice the
embodiments disclosed herein, including making and using any devices or
systems and performing the methods. The patentable scope of the subject
matter is defined by the claims, and may include other examples that
occur to one of ordinary skill in the art. Such other examples are within
the scope of the claims if they have structural elements that do not
differ from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from the
literal language of the claims.